the issue is... due you have a rear hyd remote? or some place to hook up an additional hyd unit? looking at specs, 42net HP engine, ya have weight and traction way covered.
but with only a simple draw bar. and weight of stuff you could toss on behind it.... it sure would be nice to have an hydraulic gauge wheels or running wheels or some sort of wheels to help raise/lower it. without getting off and using old hand crank style of method to raise/lower wheels.
you have 3 other tractors, size something for one of them, for a pull behind disc. and i would imagine the dozer would take what ever ya give it. actually dozer might be able to take something slightly larger, now that i look at tractordata for other tractors, due to just pure weight and traction dozer has. but seems kinda silly sizing a disc just for dozer, when you could run it behind one of the other tractors as well.
personally would be more interested in rippers / large sacrifice teeth like a box blade might have. for rear end of dozer. but i can also understand wanting a disc. to kinda slightly till the top 1/2" to 1" of the soil and then at same time almost even everything out nice and flat (with in reason of what a disc can do by itself), i tend to run the disc i have, with extra weight on it, and then at higher speeds. so i get more tossing of dirt around to smooth things out. vs at slower speeds that causes more tilling / turning of the soil.